Rapid climate change poses ecological questions

A male Liolaemus tenuis, an egg-laying lizard species broadly distributed in Central-Southern Chile. Many lizards are ectothermic, or cold-blooded, and those that live in the tropics have had their metabolic rates affected more by increased global temperatures since 1960 than those in colder regions. Credit: P. Victoriano

Although climate changes have happened throughout the Earth’s history, and species have either evolved to cope or perished, the rate of the current changes could now pose a particular problem. So says George Wang, a researcher at the Max Planck Institute for Developmental Biology in Tübingen, Germany, who has been studying global warming’s effects on ectotherms, better known as “cold-blooded creatures”.

“The most worrying aspect of recent climate change is its speed,” Wang told Simple Climate. “Climate changes in the past have generally been much slower than what we see in the last 50 years, so it’s unknown how natural populations will cope. For my field – physiological ecology – the most striking impact of climate change has been to expose just how little we know about how short to mid-term temperature variability will effect populations.”

Wang and his colleagues Michael Dillon at the University of Wyoming and Raymond Huey at the University of Washington illustrated this lack of knowledge earlier this month. They published research showing that ectotherms – such as lizards – near the equator would be more affected by climate change than those in colder climes. This had been previously overlooked by scientists studying how creatures and plants would be affected by climate change, as they had focused on the colder areas.

“Until recently, most research efforts have been devoted toward mid- to high-latitude organisms, because that is where climate warming is fastest,” Wang explained. “We hope that our findings will encourage scientists to study the impacts of warming in the tropics, which are the centre of biodiversity on Earth.”

The measure with which Wang and his colleagues studied climate change was metabolic rate – how fast species consume energy. This measure effectively shows how fast organisms use up their life, as a faster metabolic rate is generally linked to a shorter lifespan. “In laboratory experiments, we certainly see that metabolic rates of ectotherms do increase exponentially with temperature,” Wang said. “We also see that metabolic rates measured in ectotherms at different temperatures in the field increase with temperature, in general. As for the direct observations showing increasing metabolic rates as the direct results of climate change, a recent study showed that metabolic rates in soil microorganisms have increased more quickly in the tropics than elsewhere.”

This kind of data allowed Wang, Dillon and Huey to construct computational models to establish what recent climate changes would have meant for ectotherms, underlining the greater impact in the tropics compared to colder areas. However, their mathematical approach played a part in the team’s choice to study ectotherms specifically, Wang explains. “We did not include endotherms – warm-blooded – organisms like birds and mammals in our study because the relationship between ambient temperature and metabolic rate in endotherms is complex and requires special models,” he said.

While it’s currently unknown whether endotherms in the tropics will see a similar effect on their metabolic rate, Wang emphasises that for many survival relies on ectotherms. “What is almost certainly true is that many endotherms utilize ectotherms as their main food source, and thus the fates of endotherms are intrinsically tied to the fates of ectotherms.”

Madagascar is already a hotspot of lizard extinctions, with 21% of local species extinct, and members of the Gekkonidae family (Pictured here: Phelsuma quadriocellata) are currently going extinct. Credit: Ignacio De la Riva

Consequently, ectotherm metabolism is just one of a number of areas where Wang can readily see climate change affecting the world.“I think we will most likely see shifts in the [geographical] ranges of insects, both beneficial and detrimental,” he says. “I also think we will also begin to see mismatches between the timing of cyclical organism events, also known as phenology. For example, plants may begin flowering before bees have built up their colonies. These are the types of problems my colleagues and I are working on now.”

Although these changes may not seem especially great in comparison to previous climate change events that have been credited with driving creatures to extinction, Wang warns not to underestimate them. “We should keep in mind what we mean when we say that species have evolved or gone extinct in response to historical climate change,” he says. “It is one thing to think of mammoths, sabre-toothed tigers, and giant sloths going extinct in the Pleistocene era. It’s another to realize that even a minor shift in mosquito prevalence, or the range of an ectothermic crop pest, could have dramatic consequences on human health and even politics.”

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